I have a non-Nokia non-Lumia Windows phone, made but by a manufacturer in India(Phone model number is Micromax Canvas Win W121). I am running Windows 8.1 Update 2. Now, I am really eager to try out windows 10 mobile, and I know I could do so using Insider Preview..But I wanted to ask if the latest insider build is stable or will it cause any problems(this being my primary phone)..Also I wanted to know that if something were to go wrong, can I restore my phone?? Windows Phone Recovery Tool doesn't have my device listed as a supported device...
The latest windows 10 build is running smoothly but you need to wait for the official release since your phone will not run the insider preview.
You can see the list of supported phones for insider preview here.
The official release will be around this month.
EDIT AGAIN: The answer below is from 2015. At this point (Nov 2016), W10M is pretty rock-solid, especially the latest release builds (the 1607 version).
I still don't recommend using the Insider Preview builds on your day-to-day device, as those builds do still sometimes have issues, although for the most part they've been functional enough. The biggest problem with them is just the regular rebooting to install updates, honestly. For the non-Insider builds, I've had no problems at all since 1607 came out.
EDIT: The below applies to 10.0.10586.11, there is a newer build that just came out but I haven't tried it yet. I still recommend waiting to learn more.
Personally, I wouldn't actually call the current W10M builds "smooth", maybe not even "safe"; I've re-flashed my phone more times in the last two weeks (which is to say, since the "RTM" build for Insider Fast came out, and the first time I tried upgrading to it) than I have in the last five years. I've experienced everything from the location service crashing and making the phone hang so hard I couldn't even forcibly reboot it, to the phone entering a BSOD loop where it crashed to bluescreen as before even getting to the lock screen. Then there's the minor everyday nuisances, like one time (after a hard-reset on W10M) that SMS backup/restore just flat out didn't work for more than about 100 old messages, not to mention the Maps app crashing about once per hour of navigation use, or the Camera app causing the phone to reboot every so often when you try to view a photo you just took (these happened on multiple flashes and have been reported by others). That's on a Lumia 1520, which is a supported model.
In short, W10M just isn't ready yet. I'd call it an early beta, actually. It's feature-complete, and everything nominally works, but it's buggy and unreliable. You definitely should not install it, in its current form, on anything that you aren't able to re-flash using a PC; one of those hangs was bad enough that the normal hard-reset-from-power-on button combination didn't even work. I wouldn't recommend installing it on any device at present, unless you need a feature only it offers or you want to test stuff on a device that is not your daily use phone.